Mobile devices are so useful because they can get on the net with their built-in wi-fi or cellular data radios. But how does this work? In iOS, we have a slew of networking APIs, each appropriate in different situations. From decades-old BSD sockets to the new-in-iOS-5 iCloud, there are a wide range of networking calls available to your app, and an equally wide range of semantics in how to use them. In this talk, we'll start with high-level abstractions like iCloud and other objects that can either load from or save to a URL, then progress down through the stack, grabbing arbitrary content from URLs, self-networking with Bonjour and Game Kit, and finally accessing the socket layer with CFNetwork and BSD sockets. iCloud sample code at: http://dl.dropbox.com/u/12216224/conferences/codemash12/bonjour-icloud/CloudNotes.zip

1. iOS Networking:
Bonjour, iCloud!
Chris Adamson • @invalidname
CodeMash 2012
Monday, January 16, 12

2. What we’ll cover
• Obvious networking APIs
• iCloud, Bonjour, GameKit, CFNetwork
• Not-so-obvious networking APIs
• Foundation, media APIs, System
Configuration
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3. The first thing your
network app should
do?
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4. Monday, January 16, 12

5. Do I have network
access at all?
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6. Reachability
• Defined in SystemConfiguration.framework
• C-based API, Obj-C wrapper available as
sample code from Apple
• Your network-based app will be
rejected if it turtles without network
access
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7. Monday, January 16, 12

8. Reachability
• Create a SCNetworkReachabilityRef from
host name (as a C string) or address (as a
sockaddr)
• Get network info with
SCNetworkReachabilityGetFlags()
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9. Reachability Flags
enum {
kSCNetworkReachabilityFlagsTransientConnection = 1<<0,
kSCNetworkReachabilityFlagsReachable = 1<<1,
kSCNetworkReachabilityFlagsConnectionRequired = 1<<2,
kSCNetworkReachabilityFlagsConnectionOnTraffic = 1<<3,
kSCNetworkReachabilityFlagsInterventionRequired = 1<<4,
kSCNetworkReachabilityFlagsConnectionOnDemand = 1<<5,
kSCNetworkReachabilityFlagsIsLocalAddress = 1<<16,
kSCNetworkReachabilityFlagsIsDirect = 1<<17,
kSCNetworkReachabilityFlagsIsWWAN = 1<<18,
kSCNetworkReachabilityFlagsConnectionAutomatic =
kSCNetworkReachabilityFlagsConnectionOnTraffic
};
typedef uint32_t SCNetworkReachabilityFlags;
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10. Reachability callbacks
• Networks come and go; your app should
handle this
• SCNetworkReachabilitySetCallback()
MyNetworkReachabilityCallBack(
SCNetworkReachabilityRef target,
SCNetworkReachabilityFlags flags,
void *info
);
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11. Monday, January 16, 12

12. http://mattgemmell.com/2011/07/25/network-link-
conditioner-in-lion/
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13. Assuming the network
is working…
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14. Say hello to iCloud
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15. The iCloud API
•
•
•
•
•
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16. iCloud: UIDocument
• iCloud does not have its own API, per se
• Special case of saving documents
• Same code to save to local or cloud
documents directory by URL
• There are also iCloud APIs for simple
key-value storage, and Core Data
persistent stores
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17. iCloud set-up
Enable iCloud for AppID in provisioning portal
Enable entitlements in .xcodeproj (also
creates .entitlements file)
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18. Browsing in iCloud
• Compose an NSMetadataQuery (from
Spotlight API)
• Include
NSMetadataQueryUbiquitousDocu
mentsScope in search scopes
• Start search (asynchronous!)
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19. -(void) refreshNotes {
NSLog (@"refreshNotes");
[self.noteDictsArray removeAllObjects];
self.currentQuery = [[NSMetadataQuery alloc] init];
// register for notifications
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(queryDidUpdate:)
name:NSMetadataQueryDidUpdateNotification
object:self.currentQuery];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(initalGatherComplete:)
name:NSMetadataQueryDidFinishGatheringNotification
object:self.currentQuery];
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20. // Configure the search predicate
NSPredicate *searchPredicate;
searchPredicate=[NSPredicate predicateWithFormat:@"%K LIKE %@",
NSMetadataItemFSNameKey, @"*.cloudnote"];
[self.currentQuery setPredicate:searchPredicate];
// Set the search scope to only search iCloud
NSArray *searchScopes;
searchScopes=[NSArray arrayWithObjects:
NSMetadataQueryUbiquitousDocumentsScope,nil];
[self.currentQuery setSearchScopes:searchScopes];
// Start the query!
[self.currentQuery startQuery];
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21. - (void)initalGatherComplete:sender; {
// Stop the query, the single pass is completed.
[self.currentQuery stopQuery];
for (int i=0; i < [self.currentQuery resultCount]; i++) {
NSMetadataItem *noteMetadata = [self.currentQuery resultAtIndex:i];
NSString *noteName = [noteMetadata
valueForAttribute:NSMetadataItemDisplayNameKey];
NSURL *noteURL = [noteMetadata valueForAttribute:NSMetadataItemURLKey];
NSDate *noteModifiedDate = [noteMetadata
valueForAttribute:NSMetadataItemFSContentChangeDateKey];
NSLog(@"%@: %@", noteName, noteURL);
NSDictionary *noteDict = [NSDictionary dictionaryWithObjectsAndKeys:
noteName, NSMetadataItemDisplayNameKey,
noteURL, NSMetadataItemURLKey,
noteModifiedDate,
NSMetadataItemFSContentChangeDateKey,
nil];
[self.noteDictsArray addObject:noteDict];
}
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22. Monday, January 16, 12

23. But what about
document contents?
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24. iCloud documents
• Subclass UIDocument (new in iOS 5)
• Override contentsForType: and
loadFromContents:ofType:error:
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25. UIDocument overrides
- (id)contentsForType:(NSString *)typeName error:(NSError **)outError {
NSLog (@"archiving: %@", self.noteDict);
return [NSKeyedArchiver archivedDataWithRootObject:self.noteDict];
}
- (BOOL)loadFromContents:(id)contents
ofType:(NSString *)typeName
error:(NSError *__autoreleasing *)outError {
BOOL success = NO;
if([contents isKindOfClass:[NSData class]] && [contents length] > 0) {
NSData *data = (NSData *)contents;
self.noteDict = [NSMutableDictionary dictionaryWithDictionary:
[NSKeyedUnarchiver unarchiveObjectWithData:data]];
success = YES;
}
NSLog (@"noteDict: %@", self.noteDict);
return success;
}
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26. Start a new document
in iCloud
NSFileManager *fm = [NSFileManager defaultManager];
NSURL *newDocumentURL = [fm URLForUbiquityContainerIdentifier:nil];
newDocumentURL = [newDocumentURL
URLByAppendingPathComponent:@"Documents"
isDirectory:YES];
// fileName calculation omitted
newDocumentURL = [newDocumentURL
URLByAppendingPathComponent:fileName];
CDMNoteDocument *doc = [[CDMNoteDocument alloc] initWithFileURL:newDocumentURL];
// Save the new document to disk.
[doc saveToURL:newDocumentURL
forSaveOperation:UIDocumentSaveForCreating
completionHandler:^(BOOL success) {
NSLog (@"new document %@ saved",
success ? @"was" : @"was not");
}];
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27. Open an existing
iCloud document
NSURL *noteURL = (NSURL*) [noteDict valueForKey:NSMetadataItemURLKey];
CDMNoteDocument *doc = [[CDMNoteDocument alloc] initWithFileURL:noteURL];
[doc openWithCompletionHandler:^(BOOL success){
NSLog (@"opening doc at %@ %@",
doc.fileURL,
success ? @"succeeded" : @"failed");
}
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28. Saving changes
[note updateChangeCount:UIDocumentChangeDone];
[note closeWithCompletionHandler:^(BOOL success) {
NSLog (@"document close was %@",
success ? @"successful" : @"not successful");
}];
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29. Detecting iCloud
conflicts
• Register for NSNotificationCenter for
UIDocumentStateChangedNotification
• Inspect the documentState property for
the value UIDocumentStateInConflict
• Use NSFileVersion method
unresolvedConflictVersionsOfItemAtURL
to inspect the versions
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30. Demo: CloudNotes
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31. But what if my data
isn’t in iCloud?
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32. Networking in
Foundation
• NSURL
• Classes that load from URLs
• Property lists
• URL Loading System
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33. initWithContentsOfURL:
• Supported by NSString, NSData
• Also NSArray and NSDictionary if contents
are a property list
• These calls block!
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34. URL Loading System
• NSURL + NSURLRequest +
NSURLConnection + delegate callbacks
• connection:didReceiveResponse:,
connection:didReceiveData:, etc.
• Fairly deep HTTP support (incl.
authentication)
• Not an arbitrary socket networking API
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35. But I want to host a
server on my iPhone!
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36. CFNetwork
• C-based API, abstractions over network
protocols and BSD sockets
• Deep support for HTTP, HTTPS, FTP, DNS
• Built to work asynchronously in RunLoop-
based applications (incl. Cocoa Touch)
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37. If you must run a
server
• Create CFSocketRef with
CFSocketCreate() [or similar] setting
callbackTypes to kCFSocketAcceptCallback
• Callback receives a CFSocketNativeHandle
• From this,
CFStreamCreatePairWithSocket() to get
CFReadStreamRef and CFWriteStreamRef
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38. Network Discovery
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39. Bonjour!
• Protocol for address self-assignment and
service discovery
• Published ZEROCONF standard
• Open-source implementations for Mac,
Windows, Linux, Java
• APIs: NSNetService and CFNetServiceRef
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40. Searching for Bonjour
http servers
-(void) startSearchingForWebServers {
! NSNetServiceBrowser bonjourBrowser = [[NSNetServiceBrowser alloc] init];
! [bonjourBrowser setDelegate: self];
! [bonjourBrowser searchForServicesOfType:@"_http._tcp" inDomain:@""];
}
- (void)netServiceBrowser:(NSNetServiceBrowser *)netServiceBrowser
didFindService:(NSNetService *)netService
moreComing:(BOOL)moreServicesComing {
! [discoveredWebServices addObject: netService];
! [tableView reloadData];
! if (! moreServicesComing)
! ! [activityIndicator stopAnimating];
}
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41. Got a service,now
what?
• Bonjour provides the discovery, not the
service itself
• The NSNetService object includes
addresses, host name, and port
• Client connects to the host via
NSURLConnection, CFNetwork, etc.
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42. GameKit
• Simplified Bonjour over Bluetooth or WiFi
• GKPeerPickerController UI for peer
discovery
• APIs allow client-server or peer-to-peer
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43. GKSession
• All about the delegate callbacks:
• didReceiveConnectionRequestFromPeer:
• peer:didChangeState:
• receiveData:fromPeer:inSession:
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44. Demo (if we are really,
really lucky)
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45. GameKit voice chat
• Set up through Game Center
• Create with -[GKMatch
voiceChatWithName:]
• Does anyone use this?
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46. Speaking of media…
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47. HTTP Live Streaming
• Firewall-friendly audio/video streaming for
iOS and Mac OS X 10.6+ (replaces RTP/
RTSP)
• Required for any app that streams more
than 10MB over mobile network
• Client support: AVPlayer,
MPMoviePlayerController
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48. HLS: How It Works
• Segmenting server splits source media into
separate files (usually .m4a for audio-
only, .ts for A/V), usually 10 seconds each,
and creates an .m3u8 playlist file
• Playlist may point to bandwidth-appropriate
playlists
• Clients continually reload playlist, fetch the
segments, queue them up
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49. Sample playlist
#EXTM3U
#EXT-X-TARGETDURATION:8
#EXT-X-MEDIA-SEQUENCE:0
#EXTINF:8,
0640/0640_090110_120505_0.ts
#EXTINF:8,
0640/0640_090110_120505_1.ts
#EXTINF:8,
0640/0640_090110_120505_2.ts
#EXTINF:8,
0640/0640_090110_120505_3.ts
#EXTINF:8,
0640/0640_090110_120505_4.ts
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50. Bandwidth-delimited
playlist
#EXTM3U
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=1280000
http://example.com/low.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=2560000
http://example.com/mid.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=7680000
http://example.com/hi.m3u8
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51. Demo: HLS bandwidth
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52. Takeaways
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53. iOS Priorities
• Asynchronicity — don’t block the UI
• Many network APIs are difficult or
impossible to block on
• Domain-appropriate abstractions
• iCloud, GameKit, HLS
• You don’t need to know the difference
between cellular and wifi
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54. End of line.
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